The present invention relates generally to combustion gas turbine engines (or “gas turbines”), and, more specifically, but not be way of limitation, to flowpath boundary assemblies within gas turbines.
Gas turbines are widely utilized in fields such as power generation. A conventional gas turbine, for example, includes a compressor, a combustor, and a turbine. Gas turbines may further include a rotor with various rotor blades mounted to rotor wheels in the compressor and turbine sections thereof. Each rotor blade includes an airfoil over which pressurized air or fluid flows, and an inner sidewall or platform at the base of the airfoil that defines the radial boundary for the air or fluid flow therethrough. In certain turbine engine configurations, the blades are loaded into slots formed in the rotor wheel. The blades must be retained in the slots so as to prevent any radial or axial movement of the blades during operation of the turbine. Typically, dovetail mountings on the blades and complimentary dovetail slots in the wheel serve to prevent radial movement. A retention system may be utilized to ensure the rotary blades remain coupled to the rotor. However, to the extent that these retention systems include complex arrangements, production and maintenance costs may quickly escalate.
Further, the passages between adjacent blades require a smooth surface for forming the radially inner boundary of the annulus so to ensure the clean flow of air through the stage during operation. It is not preferable for the blades or the rotor wheel to accommodate this surface and usually a so called “annulus filler” is provided to bridge the annulus gap between adjacent rotor blades. It is known to provide such annulus fillers with features for removably attaching them to the rotor disc. Annulus fillers, thus, are usually manufactured from relatively lightweight materials and, in the event of damage, may be replaced independently of the blades. As a rotating component, a lighter weight filler will have lower internal forces during engine operation and also reduce forces transmitted to the rotor disc. Additionally, a smaller component mass is of benefit in reducing the overall weight of the engine and contributing to improved engine efficiency. However, an annulus filler must still be a robust component to meet operational demands and function properly under a variety of operating extremes.
A number of methods exist for mounting the annulus filler. However, as will be appreciated, there are many competing and variable design considerations that make optimization a constant objective. For example, the engagement feature must be able to withstand considerable wear and corrosion, including the extreme mechanical and thermal stresses caused by friction and heat cycling associated with the flowpath of the engine. Additionally, during engine operation the circumferential distance of the annulus gap may vary due to vibrations, twisting of blades, and relative movement between adjacent blades. In the extreme, the annulus filler may be subject to forces and relative movement between rotor blades, which can reduce the life of the rotor wheel and necessitate regular inspection during the lifetime of assembly. Furthermore, conventional manufacturing processes for rotor wheels limit the types of configurations for the connectors. As will be appreciated, requiring additional features or weight on the rotor wheel gives rise to design and manufacturing considerations to control stress in the component, and any features that add complexity may be cost prohibitive to manufacture.
Thus, an improved retention devices and assemblies for annulus filler and rotor blade assemblies would be desired in the art. For example, an axial retention device that prevents axial movement of the blades and/or annulus filler components with respect to the rotor wheels and other support structures would be advantageous. Further, a retention devices that provides for efficient and cost-effective replacement of the blades, annulus fillers, and/or other related components, and that reduces or eliminates the need to replace the rotor wheels and other support structures, would be desired.